Method for producing single-sided sputtered magnetic recording disks

ABSTRACT

An information-storage media is provided that includes:
         (a) a substrate disk  312  having first and second opposing surfaces;   (b) a first selected layer  304  on the first surface, the first selected layer having a first thickness;   (c) a second selected layer  308  on the second surface, the second selected layer having a second thickness, wherein the first and second selected layers have a different chemical composition than the substrate disk; and   (d) an information-storage layer  412  adjacent to one or both of the selected layers.
 
The first and second thicknesses are different to provide an unequal stress distribution across the cross-section of the media.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional under 35 U.S.C. §120 of U.S.patent application Ser. No. 11/195,912, filed Aug. 2, 2005, now U.S.Pat. No. 7,267,841 which is a divisional under 35 U.S.C. 120 of U.S.patent application Ser. No. 10/434,550, filed May 9, 2003, now U.S. Pat.No. 7,083,871 which claims the benefits of U.S. Provisional ApplicationSer. Nos. 60/379,007 to Kim et al., and 60/378,967 to Kim, both of whichwere filed on May 9, 2002, each of the foregoing applications areincorporated herein by this reference.

The subject matter of the present application is related to thefollowing applications, each of which has a filing date of May 9, 2003:entitled Dual Disk Transport Mechanism Processing Two Disks TiltedToward Each Other to Grow et al.; entitled Information-Storage MediaWith Dissimilar Outer Diameter and/or Inner Diameter Chamfer Designs OnTwo Sides to Clasara et al.; entitled Method of Merging Two DisksConcentrically Without Gap Between Disks to Buitron; entitled Apparatusfor Combining or Separating Disk Pairs Simultaneously to Buitron et al.;entitled Method of Simultaneous Two-Disk Processing of Single-SidedMagnetic Recording Disks to Buitron et al.; entitled W-Patterned Toolsfor Transporting/Handling Pairs of Disks to Buitron et al.; entitledMethod for Servo Pattern Application on Single-Side Processed Disks in aMerged State to Valeri; entitled Method for Simultaneous Two-DiskTexturing to Buitron et al.; entitled Cassette for Holding Disks ofMultiple Form Factors to Buitron et al.; entitled Automated Merge Nestfor Pairs of Magnetic Storage Disks to Crofton et al.; entitledApparatus for Simultaneous Two-Disk Scrubbing and Washing to Crofton etal.; entitled Cassette Apparatus for Holding 25 Pairs of Disks forManufacturing Process to Buitron et al.; and entitled Method ofLubricating Multiple Magnetic Storage Disks in Close Proximity toBuitron et al. Each of these applications is incorporated by referencein its entirety as if stated herein.

FIELD OF THE INVENTION

The present invention is related generally to recording media andspecifically to single-sided magnetic recording media.

BACKGROUND OF THE INVENTION

Hard disk drives are an efficient and cost effective solution for datastorage. Depending upon the requirements of the particular application,a disk drive may include anywhere from one to twelve hard disks and datamay be stored on one or both surfaces of each disk. While hard diskdrives are traditionally thought of as a component of a personalcomputer or as a network server, usage has expanded to include otherstorage applications such as set top boxes for recording and timeshifting of television programs, personal digital assistants, cameras,music players and other consumer electronic devices, each havingdiffering information-storage capacity requirements.

As aerial bit densities of hard disks have dramatically increased inrecent years, the large data storage capacities of dual-sided magneticstorage media far exceed demand in many applications. For example,dual-sided hard disks in personal computers have much greater storagecapacity than most consumers require during the useful life of thecomputer. Consumers thus are forced to pay substantial amounts forexcess data storage capacity. The intense price competition in themagnetic storage media industry has forced many disk drive manufacturersto offer single-sided magnetic storage media as an alternative.Single-sided storage media are of two types. In one type, a double-sideddisk configured to store information on both sides of the disk isinstalled with a single read/write head serving only one side of thedisk. In the other type, known as a single-sided processed disk, onlyone side of the disk is provided with an information-containing magneticlayer. The other side of the disk does not have aninformation-containing layer. Single-sided processed disks not only havesufficient storage capacities to satisfy most consumers but also can bemanufactured at lower costs than dual-sided disks due to reducedmaterial usage. Nonetheless, there is an ongoing need for less expensivestorage media.

SUMMARY OF THE INVENTION

A single-sided processed disk has been developed to provide a low coststorage media. A recurring problem with the single-sided processed disksis the degree of planarity or flatness of the disk. Referring to FIGS. 1and 2, a single-sided processed magnetic recording disk 100 isillustrated. The disk 100 includes a substrate disk 200 (which istypically aluminum or an aluminum alloy), upper and lower selectedlayers 204 and 208 (which are typically nickel phosphorus), anunderlayer 212 (which is typically chromium or a chromium alloy), amagnetic layer 216 (which typically is a cobalt-platinum-basedquaternary alloy having the formula CoPtXY or a five element alloyCoPtXYZ, where XY and Z can be tantalum, chromium, nickel or boron), anovercoat layer 220 (which is typically carbon), and a lubricant layer224 (which is typically a perfluoropolyether organic polymer). Thenickel phosphorus layers have the same thicknesses, “t_(u)” (upper layerthickness) and “t_(L) (lower layer thickness), (each of which istypically from about 8 to about 15 micrometers) and are typicallydeposited by electroless plating techniques. The underlayer, magneticlayer, and overcoat layer have different thicknesses (their totalthickness is typically from about 20 to about 100 nm) and are depositedby sputtering techniques. Although nickel phosphorus layers can bedeposited in either compression or tension, they are typically depositedin compression and the sputtered layers are also typically deposited incompression. As can be seen from FIG. 2, the compressive forces in thelower nickel phosphorus layer 208 are more than offset by thecompressive forces in the upper nickel phosphorus layer 204 and thesputtered layers 212, 216 and 220, causing the disk 100 to be concave onthe upper side 228 of the disk and convex on the lower side 232.

The disk concavity on the infonnation storing side of the disk can causeproblems. Disk concavity can cause problems in read/write operations,such as due to head tracking errors and undesired contact of the headwith the disk surface. Because of these issues, typical diskspecifications require a flatness on the information-containing oractive surface of the disk of no more than about 7 to about 15 microns.As will be appreciated, “flatness” refers to the distance between thehighest and lowest points on a disk surface. With reference to FIG. 2,the flatness is the difference in the elevations of points 1 and 2,where point 1 is the lowest point on upper disk surface 228 while point2 is the highest point on the upper disk surface 228.

These and other needs are addressed by the various embodiments andconfigurations of the present invention. The present invention isdirected generally to controlling the stresses (either compressiveand/or tensile) in the layers/films deposited on either side ofinfonnation-storage media to produce a desired degree of flatness orshape in the media.

In one aspect of the present invention, an information-storage media isprovided that includes:

(a) a substrate disk having first and second opposing surfaces;

(b) a first selected layer on the first surface;

(c) a second selected layer on the second surface; and

(d) an information-storage layer adjacent to one or both of the selectedlayers. The first selected layer has a first thickness, and the secondlayer a second thickness. The first and second selected layers have adifferent chemical composition than the substrate disk, which typicallycause the selected layers to have a differing magnitude of internalcompressive or tensile stress than is present in the substrate disk. Inother words, the stress distribution across the thickness of the mediais non-uniform. To provide a desired disk shape, the first and secondthicknesses are different, causing a desired balance or imbalancebetween compressive/tensile stresses on either side of the substratedisk. As shown in the figures and discussed below, it is to beunderstood that the “selected layer” may or may not be positionedbetween other layers. In one configuration, the selected layer isconfigured as a backing layer on a reverse side of the disk.

In one media configuration, the first thickness is no more than about99.3% of the second thickness, and the difference in thickness betweenthe first and second selected layers is at least about 0.075 microns.Although the selected layer adjacent to the information-storage layer isnonnally thinner than the nonadjacent selected layer, it may bedesirable to have the thicker selected layer adjacent to theinformation-storage layer.

Preferably, the first and second selected layers comprise nickelphosphorus. Although the first and second selected layers typically havethe same chemical composition, there may be applications where differingmaterials are used in the two layers.

The information-storage layer can store information by any suitableteclmique, such as by optical, magneto-optical, or magnetic techniques.The material in the layer can be a thin film, a thick film, or a bulkmaterial. Preferably, the information-storage layer is a thin filmferromagnetic material.

The media can include other layers. For example, an underlayer may bepositioned between the information-storage layer and the first selectedlayer, and an overcoat layer above the information-storage layer. Thematerials in the layers can be thin films, thick films, or bulkmaterials. In one media configuration, the information-storage layer,underlayer, and overcoat layer are each thin films and in compression.In other media configurations, one or more of the layers can be intension.

In one media configuration, the first selected layer is positionedbetween the information-storage layer and the substrate disk while thesecond surface is free of an information-storage layer. So configured,the disk has one active side and one inactive side. The medium can besingle- or dual-sided. In other words, one or both surfaces of themedium can be “active”. As used herein, “active” or“information-containing” means that the disk surface is configured tostore data. As used herein, “inactive”, “non-active,” or“noninformation-containing” means that the medium surface is notconfigured to store data. For example, the active side of the medium hasan information storage layer(s), such as a magnetic layer, while theinactive side of the medium has no information storage layer(s).

In another aspect, a method for manufacturing a single-sidedinformation-storage media is provided that includes the steps of:

(a) providing first and second intermediate structures, each of thefirst and second intermediate structures comprising substrate disks andupper and lower selected layers on opposing upper and lower sides,respectively, of each substrate disk;

(b) placing the lower selected layer of the first intermediate structureadjacent to the lower selected layer of the second intermediatestructure, such that the first and second intermediate structures are ina stacked relationship; and

(c) simultaneously removing at least a portion of each of the upperselected layers of the first and second intermediate structures while inthe stacked relationship to provide, for each of the first and secondintermediate structures, upper and lower selected layers havingdifferent thicknesses.

The present invention can have a number of advantages compared toconventional storage media configurations and fabrication processes. Forexample, disk concavity on the infonnation storage side of a disk can becontrolled, thereby avoiding problems in read/write operations, such asdue to head tracking errors and undesired contact of the head with thedisk surface. In particular, single-sided media can have reducedflatness values by eliminating the systematic stress imbalance acrossthe disk cross-section. The final storage media can be consistently andrepeatedly provided with a flatness in compliance with ever decreasingdisk specifications, which currently require a maximum flatness on theinformation-containing surface of the disk in the range of about 7 toabout 15 microns. The ability to control the flatnesses of theintermediate and final media permit manufacturers to produce media withdesired shapes, e.g., flatnesses, for a wide variety of applications.For example, single-sided and dual-sided disks can both be provided witha desired degree of concavity or convexity. To provide a more curvedshape, a stress imbalance can be introduced between the two sides of themedia. The ability to remove simultaneously from two stacked mediadiffering thicknesses of selected layer can provide substantial cost andthroughput savings compared to conventional one-at-a-time diskprocessing. The use of a thicker carrier during rough and/or finepolishing can permit a manufacture to use existing media polishingmachinery and materials to effect two-disk-at-a-time polishing.

These and other advantages will be apparent from the disclosure of theinvention(s) contained herein.

The above-described embodiments and configurations are neither completenor exhaustive. As will be appreciated, other embodiments of theinvention are possible utilizing, alone or in combination, one or moreof the features set forth above or described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a disk;

FIG. 2 is a cross-sectional view along disk center line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along the disk center line of aplated disk according to an embodiment of the present invention;

FIG. 4 is a cross-sectional view taken along the disk center line of asputtered disk based on the plated disk of FIG. 3;

FIG. 5 is a flow chart of a substrate disk process according to anembodiment of the present invention according to an embodiment of thepresent invention;

FIGS. 6A and B are cross-sectional views taken along a center line of adisk polishing assembly;

FIG. 7 is a flow chart of a media process according to an embodiment ofthe present invention;

FIG. 8 is a cross-sectional view taken along the disk center line of aplated disk according to an embodiment of the present invention;

FIG. 9 is a cross-sectional view taken along the disk center line of aplated disk according an embodiment of the present invention;

FIG. 10 is a cross-sectional view taken along the disk center line of asputtered disk based on the disk of FIG. 9;

FIGS. 11A and 11B depict a plated and polished disk manufactured by afirst experimental process;

FIGS. 12A and 12B depict a plated and polished disk manufactured by thefirst experimental process;

FIGS. 13A and 13B depict a plated and polished disk manufactured by thefirst experimental process;

FIGS. 14A and 14B depict a plated and polished disk manufactured by thefirst experimental process;

FIGS. 15A and 15B depict a plated and polished disk manufactured by thefirst experimental process;

FIGS. 16A and 16B depict a plated and polished disk manufactured by asecond experimental process;

FIGS. 17A and 17B depict a plated and polished disk manufactured by thesecond experimental process;

FIGS. 18A and 18B depict a plated and polished disk manufactured by thesecond experimental process;

FIGS. 19A and 19B depict a plated and polished disk manufactured by thesecond experimental process;

FIGS. 20A and 20B depict a plated and polished disk manufactured by thesecond experimental process;

FIGS. 21A and 21B depict a sputtered disk of a Type A configuration;

FIGS. 22A and 22B depict a sputtered disk of the Type A configuration;

FIGS. 23A and 23B depict a sputtered disk of the Type A configuration;

FIGS. 24A and 24B depict a sputtered disk of the Type A configuration;

FIGS. 25A and 25B depict a sputtered disk of the Type A configuration;

FIGS. 26A and 26B depict a sputtered disk of the Type A configuration;

FIGS. 27A and 27B depict a sputtered disk of a Type B configuration;

FIGS. 28A and 28B depict a sputtered disk of the Type B configuration;

FIGS. 29A and 29B depict a sputtered disk of the Type B configuration;

FIGS. 30A and 30B depict a sputtered disk of the Type B configuration;

FIGS. 31A and 31B depict a sputtered disk of the Type B configuration;and

FIGS. 32A and 32B depict a sputtered disk of the Type B configuration.

DETAILED DESCRIPTION

Referring to FIG. 3, a first embodiment of a disk according to thepresent invention will be described. Although the invention is describedwith specific reference to a magnetic recording disk, it is to beunderstood that the principles of the present invention may be extendedto other recording media types, such as optical recording media, andmagneto-optical recording media, and can be used for floppy or harddisks.

FIG. 3 depicts a plated disk (or intermediate (disk) structure) 300having upper and lower selected layers 304 and 308, respectively, on asubstrate disk 312. The substrate disk can be any suitable substratedisk, such as aluminum, aluminum alloys (e.g., AlMg), glass, ceramicmaterials, titanium, titanium alloys and graphite. The interface layerscan be any suitable material for achieving acceptable magnetic recordingproperties in the overlying magnetic layer(s), such as iron oxide,nickel phosphorus, nickel molybdenum phosphorus, and nickel antimonyphosphorus, with the latter three materials being preferred. Theselected layers 304 and 308 are typically the same chemical compositionand have different compositions from the substrate disk to provide anuneven internal stress distribution across the disk cross-section.

As can be seen from FIG. 3, the thicknesses of the upper and lowerselected layers 304 and 308, which are t_(U) and t_(L), respectively,are different. When the selected layers are deposited so as to be incompression or have internal compressive stress, the thickness t_(U) ofthe upper selected layer 304 which is to become the surface forsputtering of the underlayer, magnetic layer, and overcoat layer, ispreferably less than the thickness t_(L) of the lower selected layer308. This causes the disk 300 to be curved (e.g., have a sphericalcurvature) in cross-section or have a bowl-shape, with the concave sideof the disk 300 being the surface on which the additional layers are tobe sputtered. This is so because the compressive stress in the thickerlower selected layer 308 exceeds the compressive stress in the thinnerupper selected layer 304, thereby causing the disk to be warped towardsthe thinner selected layer.

The governing equations for this behavior are set forth below.

The stress ε in a selected layer is determined by the unique physicalproperties of a material and the technique and conditions of deposition:

The spherical curvature or radius of curvature R of the disk is providedby the following equation.R=t _(sub) ²/(6×Δt _(layer)×ε)where t_(sub) is the thickness of the substrate disk 312, Δt_(layer) isthe difference in thicknesses between the upper and lower selectedlayers 304 and 308, and ε is the stress in each of the layers.

While the relative thicknesses of the two layers depends on themagnitude of the internal compressive stress in each layer and thecompressive stresses in the sputtered layers, the thickness of the upperselected layer 304 is typically no more than about 99.3%, more typicallyfrom about 98.3 to about 99.3% and even more typically from about 97.7to about 98.3% of the thickness of the lower selected layer 308. Inabsolute terms, the thickness of the upper selected layer 304 rangesfrom about 7.5 to about 14.5 microns and that of the lower selectedlayer 308 from about 8 to about 15 microns. In other words, thedifference in thickness between the upper and lower selected layers istypically at least about 0.075 microns and more typically ranges fromabout 0.2 to about 2 microns.

The flatness (or first flatness) of the disk 300 is relatively high andthe flatness distribution, 3σ, is relatively low. The flatness of eachof the upper and lower surfaces 316 and 320, respectively, of the disk300 typically is at least about 5 microns and more typically ranges fromabout 2 to about 10 microns.

FIG. 4 depicts the same disk 400 after deposition of the overlyinglayers. Specifically, the upper surface 404 of the disk 400 has theunderlayer 408, the magnetic layer 412, and the overcoat layer 416deposited, preferably by sputtering. The underlayer 408 can be anymaterial capable of providing the desired crystallography in themagnetic layer 412. Preferably, the underlayer 408 is chromium or achromium alloy and has a thickness ranging from about 5 to about 20 nm.The magnetic layer 412 can be any ferromagnetic material, with thecobalt-platinum-based quaternary alloy having the formula CoPtXY or thefive element alloy CoPtXYZ, wherein XY and Z can be tantalum, chromium,boron, or nickel. The thickness of the magnetic layer typically rangesfrom about 7 to about 20 nm. The overcoat layer 416 can be any suitableovercoat material, with carbon being preferred, and the thickness of thelayer typically ranges from about 1 to about 6 nm.

The layers are typically in compression or have internal compressivestresses. The stress in each layer can be calculated using the equationabove. The cumulative magnitude of the compressive stresses in the upperselected layer 304, the underlayer 408, the magnetic layer 412, and theovercoat layer 416 counteract the compressive stress in the lowerselected layer 308 to cause the disk to flatten out or become moreplanar. For a given thickness of the lower selected layer 308, theresulting radius of curvature of the disk is inversely proportional tothe cumulative thicknesses of the layers 304, 408, 412, and 416.Typically, the flatness of the disk 400 (or second flatness) is no morethan about 17 microns and more typically is no more than about 12microns.

The relative magnitudes of the cumulative compressive stress in theupper layers 304, 408, 412, and 416 versus that in the lower selectedlayer 308 may be controlled to provide a desired degree of flatness inthe final disk. For example, when the cumulative compressive stress inthe upper layers exceeds that in the lower selected layer, the uppersurface 404 of the disk will be convex with the opening of thebowl-shape facing downward. When the cumulative compressive stress inthe upper layers is less than that in the lower selected layer, theupper surface 404 of the disk will be concave with the opening of thebowl-shape facing upward. When the cumulative compressive stress in theupper layers is approximately equal to that in the lower selected layer,the upper surface 404 of the disk will be substantially or completelyflat or planar as shown in FIG. 4. By these techniques, disks of varyingradii of curvature and flatnesses can be produced. Typically, theflatness values can be made to range from about 1 to about 50 microns.

The control of the radius of curvature or flatness of the disk can beimportant. Not only is it important for the disk to comply withpertinent flatness specifications but also as the disk temperaturefluctuates during read/write operations due to disk rotation the diskcurvature changes. For example, the disk may become more concave orconvex depending on the rate of change of the compressive stress of eachlayer due to thermal fluctuations. In one configuration, it is desirablefor the disk to be more convex at higher operating temperatures and moreconcave at lower operating temperatures.

As seen in FIG. 8, for example, the thickness of the upper selectedlayer 804 can be selected to be thicker than that of the lower selectedlayer 808 to provide a convex upper disk surface 800. This surface willbecome even more convex when the underlayer, magnetic layer, andovercoat layer are deposited on the upper disk surface. In oneconfiguration, the underlayer, magnetic layer, and overcoat layer aredeposited so as to have a net internal tensile stress. This can beeffected by selecting suitable materials for each layer and/or by usinga suitable deposition technique other than sputtering. In thatconfiguration, the use of an upper selected layer having a greaterthickness than that of the lower selected layer may be used tocounteract the tensile stress to provide the desired degree of disksurface flatness.

When nickel phosphorus is the selected layer on both sides of the disk,it is possible to deposit the layers with a desired degree of internalcompressive or tensile stress by varying the composition of theelectroless plating bath. When the layers are in tensile as opposed tocompressive stress, the use of an upper selected layer 904 that isthinner than the lower selected layer 908 will, as shown in FIG. 9,cause the upper disk surface 912 to be convex. To offset this effect,the underlayer, magnetic layer, and overcoat layer, which are incompressive stress, are preferably deposited on the side having thethicker selected layer, which in the configuration of FIG. 9 is thelower selected layer 908. The tensile force exerted by the sputteredlayers and the compressive force exerted by the upper selected layeroffsets the tensile force exerted by the lower selected layer to providea relatively planar disk 1000 as shown in FIG. 10.

An embodiment of the process to produce the disk of FIGS. 3 and 4 willnow be discussed with reference to FIGS. 5 and 6.

Referring to FIG. 5, the substrate disk process will first be discussed.In step 500, the disk substrate disk 312 is stamped out of a sheet ofmaterial. The stamped disk in step 504 is ground to provide flat orplanar upper and lower substrate disk surfaces. In step 508, the disk isbaked, and in step 516 chamfers are formed on the upper and lowersubstrate disk surfaces. In step 520, the upper and lower selectedlayers, which are nickel phosphorus, are formed on the upper and lowersubstrate disk surfaces by electroless plating techniques. In this step,the thicknesses of the upper and lower selected layers are the same orsubstantially the same. Typically, the thickness of the upper selectedlayer is at least about 95% of the thickness of the lower selected layerand vice versa. Steps 500 through 520 are performed using techniquesknown to those of skill in the art.

In steps 524 and 528, the selected layers are rough (step 524) and fine(step 528) polished to provide the plated disk configuration of FIG. 3.As shown in FIG. 6A, in each of steps 524 and 528 a disk holder 600contains compartments (or holes) for receiving two disks simultaneously(referred to as “two-at-a-time disk polishing”). Upper and lowerpolishing pads 604 and 608 polish the outwardly facing surfaces 612 and616 of the adjacent stacked disks 620 a, b. The contacting disk surfaces624 and 628 are not polished. The polished surfaces 612 and 616 are theupper disk surface 316 in FIG. 3. In this manner, two adjacent orstacked disks are polished simultaneously to provide a significant costsavings relative to the costs to produce dual-sided disks.

Preferably, the reduction in thickness of the upper selected layer is atleast about 0.70% and more preferably ranges from about 1.0 to about4.0%.

There are several ways to effect the reduction in layer thicknessreduction in the polishing steps. In one approach, all of the thicknessdifference between the upper and lower selected layers is effected inthe rough polishing step 524. In a second approach, all of the thicknessdifference between the upper and lower selected layers is effected inthe fine polishing step 528. These two approaches require both sides ofthe disk to be polished in one of the polishing steps, which can becostly. The polishing in this step is performed using one-disk-at-a-timepolishing as shown in FIG. 6B. Referring to FIG. 6B, upper and lowerpolishing pads 604 and 608 engage simultaneously the upper and lowersides 704 and 708 of each disk 700. The carrier 712 transports the disksthrough the polishing operation. In a third approach, a portion of thethickness difference between the upper and lower selected layers iseffected in each of the rough and fine polishing steps. In thisapproach, the disks remain in the carrier 600 (FIG. 6A) through each ofthe polishing steps, which can represent a significant cost savingsrelative to the other two approaches.

In one process configuration, the thickness of the upper and lowerselected layers 304 and 308 is the same after step 520 and range fromabout 8 to about 15 microns. In the rough polishing step 524, from about70 to about 95% of the desired thickness reduction in the upper selectedlayer 304 is realized. The remaining desired thickness reduction in theupper selected layer 304 is realized in the fine polishing step 528.

After the fine polishing step 528, the plated disk is sent to the mediaprocess.

The media process will be discussed with reference to FIG. 7.

In step 700, the plated disks are merged for processing. “Merging”refers to placing the disks back-to-back such that the upper disksurfaces 316 face outwardly. In other words, the lower disk surfaces 320are adjacent to one another. The disks can be contact merged (as shownin FIG. 6A) in which case the lower disk surfaces 320 of each disk 300physically contact one another or gap merged in which case the lowerdisk surfaces 320 of each disk 300 are separated by a gap.

In step 704, the upper disk surfaces 316 are data zone textured by knowntechniques.

In step 708, the upper disk surfaces 316 are washed to remove any debrisor contaminants from the data zone texturing step.

In step 712, the upper disk surfaces 316 are layer zone textured byknown techniques followed by washing of the upper disk surfaces in step716.

In step 720, the underlayer 408, magnetic layer 412, and overcoat layer416 are sputtered onto the upper disk surface by known techniques toproduce the disk configuration of FIG. 4. As noted previously, thesputtered layers cause the disk curvature to flatten out. Othertechniques can be used to deposit these layers, such as evaporationtechniques, ion beam techniques, plating techniques, and the like.

The disk is then subjected to the application of a lubrication layer(such as an organic polymer, e.g., a perfluoropolyether) in step 724 andtape burnishing in step 728. Steps 724 and 728 are performed bytechniques known to one of skill in the art.

In step 732, the adjacent disks are separated or demerged to provide thefinished disk 736. The lower side 420 of the disk is the “inactive” ornon-information storing side while the upper side 404 of the disk is the“active” or information storing side.

EXPERIMENTAL

A number of experiments were performed to illustrate the principles ofthe present invention. In a first series of experiments, variousmagnetic disks were made using both one-at-a-time and two-at-a-time diskpolishing to evaluate the varying degrees of flatness of the disks andthe use of such polishing techniques in the fine and rough polishingsteps.

Type 1 disks were formed by electroless plating of nickel phosphorous(NiP) on both sides of aluminum magnesium (AlMg) disks. The NiP layerson both sides of the disks were equal and about 500μ. The concavity ofthe disks was approximately 5μ. The disk thickness was about 50 mil witha 95 mm outer diameter (OD) and 25 mm inner diameter (ID). The Type 1disks were rough-polished using one-at-a-time polishing (as shown inFIG. 6B) maintaining equal removal of nickel material or both sides. Therough-polished substrate disks were then washed thoroughly and ensuredto be virtually free of particulates. Washing of the disks minimizesformation of deep scratches during the final step polishing on thenon-information-storing side (or inactive side). Such scratches usuallypenetrate on the information-storing side (or active side). The washedsubstrate disks are kept fully immersed in distilled water until readyfor the final polishing step.

The final polishing step is performed by loading 2-disks at a time inthe carrier hole, as shown in FIG. 6A. The carrier 600 is designed toaccommodate the thickness of the two disks. The removal of the nickelmaterial takes place only on one side of each disk during this finalpolishing step. By adjusting polishing time, the NiP thickness deltabetween the active and inactive sides and the resulting degree ofconcavity of the substrate disk can both be controlled.

The process variables in the rough and fine polishing steps are asfollows:

Machine/Process Set-up Conditions:

-   -   Pressure: 180˜220 dAN    -   Rotation: 14˜20 rpm    -   Slurry for the Rough Polish: Aluminia (˜0.45μ″ size)    -   Slurry for Final Polish: Colloidal silica (35˜100 nm size)    -   Machine type used: Peter Wolters AC319™ Disk Polishing Machine

The intended thickness differential in the NiP layers on the active andinactive sides was about 10 to about 20μ″, with the active side havingthe thinner NiP layer. The carrier had six carrier holes, eachaccommodating a single disk, in the rough polishing step and six holes,each accommodating two disks, in the fine polishing step. The thicknessof the carrier was about 40 mil for the rough polishing step and about90 mil for the fine polishing step. For each run, nine carriers wereused.

Type 2 disks were formed by electroless plating of nickel phosphorous(NiP) on both sides of aluminum magnesium (AlMg) disks. The NiP layerson both sides of the disks were equal and about 500μ. The concavity ofthe disks were approximately 35μ. The disk thickness was about 50 milwith a 95 mm outer diameter (OD) and 25 mm inner diameter (ID).

The plated substrate disks were rough-polished by two-disk-at-a-timepolishing techniques, such that two disks at a time were loaded in thesame or a common carrier hole. The rough polishing step was thusdifferent than the rough polishing step for Type 1 disks, in whichone-disk-at-a-time polishing techniques were employed. The removal ofthe nickel material occurred on only one side of each disk during therough polishing step. The washing and fine polishing steps were the sameas the steps used for the Type 1 disks.

The process variables were the same as those shown above for Type 1 diskfabrication except for the thickness differential between the NiP layerson the active and inactive sides of the disks and the carrier thicknessin the rough polishing step. The thickness of the carrier for both therough and fine polishing steps was the same at about 90 mil.

The intended NiP thickness differential for the active and inactivesides of the disks was about 70 to about 90μ″, with the NiP layer on theactive side being thinner than the NiP layer on the inactive side.

The shape and flatness of resulting disks are shown in FIGS. 11A through15B (Type 1 disks) and FIGS. 16A through 20B (Type 2 disks). It isimportant to note that the Type 2 disk flatness plots appear to betruncated in some areas because the measurement tool limits were locallyexceeded. The Root Mean Square or RMS, Peak-to-Peak (P-V) and averageflatness (Ra) values along with the scanned area are as follows for eachfigure:

in FIGS. 11A and 11B, the RMS is 1.270 microns, the P-V is 5.167microns, the Ra is 1.093 microns, and the area scanned is the product of93.77 and 92.76 square mm;

in FIGS. 12A and 12B, the RMS is 1.221 microns, the P-V is 4.773microns, the Ra is 1.054 microns, and the scanned area is the product of93.77 and 92.76 square mm;

in FIGS. 13A and 13B, the RMS is 0.666 mm, the P-V is 2.673 mm, the Rais 0.575 mm, and the scanned area is the product of 93.77 and 92.76square mm;

in FIGS. 14A and 14B, the RMS is 1.078 microns, the P-V is 4.417microns, the Ra is 0.922 mm, and the scanned area 93.77 and 92.76 squaremm;

in FIGS. 15A and 15B, the RMS is 1.378 microns, the P-V is 5.381microns, the Ra is 1.191 microns, and the scanned area is the product of93.77 and 92.76 square mm;

in FIGS. 16A and 16B, the RMS is 361.58 microns, the P-V is 1485.83microns, the Ra is 318.23 microns, and the scanned area is the productof 91 and 86.33 square mm;

in FIGS. 17A and 17B, the RMS is 315.92 microns, the P-V is 1193.22microns, the Ra is 273.25 microns, and the scanned area is the productof 71.61 and 92.30 square mm;

in FIGS. 18A and 18B, the RMS is 363.17 microns, the P-V is 1524.48microns, the Ra is 300.23 microns, and the scanned area is the productof 48.27 and 89.54 square min;

in FIGS. 19A and 19B, the RMS is 376.56 microns, the P-V is 1424.40microns, the Ra is 324.26 microns, and the scanned area is the productof 63.70 and 86.79 square mm;

in FIGS. 20A and 20B, the RMS is 365.63 microns, the P-V is 1432.22microns, the Ra is 315.11 microns, and the scanned area is the productof 64.89 and 94.14 square mm;

in FIGS. 21A and 21B, the RMS is 1.437 microns, the P-V is 5.645microns, the Ra is 1.235 microns, and the scanned area is the product of91.00 and 90.00 square mm;

in FIGS. 22A and 22B, the RMS is 0.728 microns, the P-V is 2.870microns, the Ra is 0.626 microns, and the scanned area is the product of92.58 and 92.76 square mm;

in FIGS. 23A and 23B, the RMS is 1.265 microns, the P-V is 4.808microns, the Ra is 1.088 microns, and the scanned area is the product of91.39 and 90.46 square mm;

in FIGS. 24A and 24B, the RMS is 1.203 microns, the P-V is 4.822microns, the Ra is 1.031 microns, and the scanned area is the product of91.79 and 90.92 square mm;

in FIGS. 25A and 25B, the RMS is 1.339 microns, the P-V is 5.317microns, the Ra is 1.145 microns, and the scanned area is the product of90.60 and 91.38 square mm;

in FIGS. 26A and 26B, the RMS is 1.107 microns, the P-V is 4.192microns, the Ra is 0.956 microns, and the scanned area is the product of91.39 and 91.38 square mm;

in FIGS. 27A and 27B, the RMS is 0.128 microns, the P-V is 0.617microns, the Ra is 0.107 microns, and the scanned area is the product of93.77 and 94.14 square mm;

in FIGS. 28A and 28B, the RMS is 0.442 microns, the P-V is 2.254microns, the Ra is 0.354 microns, and the scanned area is the product of93.77 and 94.14 square mm;

in FIGS. 29A and 29B, the RMS is 0.234 microns, the P-V is 0.982microns, the Ra is 0.202 microns, and the scanned area is the product of93.77 and 94.14 square mm; in FIGS. 30A and 30B, the RMS is 0.246microns, the P-V is 1.358 microns, the Ra is 0.190 microns, and thescanned area is the product of 93.77 and 94.14 square mm;

in FIGS. 31A and 31B, the RMS is 0.592 microns, the P-V is 2.926microns, the Ra is 0.475 microns, and the scanned area is the product of93.77 and 94.14 square mm; and

in FIGS. 32A and 32B, the RMS is 0.454 microns, the P-V is 2.234microns, the Ra is 0.371 microns, and the scanned area is the product of93.77 and 94.14 square mm;

The peak-to-valley flatness values and selected layer thicknesses aresummarized in the table below.

Measured Measured NiP NiP NiP Flat- thickness thickness thickness Shapeness on A-side on B-side (A − B) Type substrate 1 concave 5.167μ 404μ″415μ″ −11μ″ 1 substrate 2 concave 4.773μ 368μ″ 375μ″  −7μ″ substrate 3concave 2.673μ 423μ″ 432μ″  −9μ″ substrate 4 concave 4.417μ 402μ″ 416μ″−14μ″ substrate 5 concave 5.381μ 400μ″ 429μ″ −29μ″ Type substrate 1concave 35.69μ 388μ″ 476μ″ −88μ″ 2 substrate 2 concave 30.31μ 410μ″485μ″ −75μ″ substrate 3 concave 38.72μ 388μ″ 480μ″ −92μ″ substrate 4concave 36.18μ nda nda nda substrate 5 concave 36.38μ nda nda nda (nda:no data available)

The average NiP thickness differential for Type 1 disk samples is about14μ″ while that for Type 2 disk samples about 85μ″. Each valuecorresponds to the amount of NiP material removed (stock removal) duringfinal polishing (Type 1 disks) and during rough and final polishing(Type 2 disks). Type 1 disks exhibited about 5μ concavity, withsimultaneous two-disks-at-a-time polishing being implemented only in thefinal polishing step. Type 2 disks exhibited about 35μ concavity, withsimultaneous two-disks-at-a-time polishing being implemented in both therough and fine polishing steps.

The degree of concavity induced as a result of uneven material removalon the active/inactive sides appears to be proportional to the NiP layerthickness differential between the two sides. Typical counterpartsubstrate disks polished utilizing conventional methods (as depicted inFIG. 6B) exhibited average flatness values of about 2μ″−(˜50% of theflatnesses being concave and ˜50% of the flatnesses being convex) andthe NiP layer thickness differential being less than about 3μ″. Strictlyspeaking, the thickness differential is the average of the absolutevalues of NiP layer thickness differentials among the various disks.Further experiments were performed to determine the degree to whichsputtered thin films can flatten pre-bent disks, such as the Type 1 and2 disks above. Two different types of magnetic recording disks werefabricated. The two different types of disks had the followingstructures:

Type A NiP layer thickness on right side: ~415 μ″ disks NiP layerthickness on left side: ~415 μ″ (control) Sputtered thin films withtotal thickness of ~300 A NiP layer thickness differential between theright and left sides: ~0 μ″ Type BNiP layer thickness on right(active)-side: ~415 μ″ disks NiP layer thickness on left(inactive)-side: ~435 μ″ Sputtered thin films with total thickness of~300 A NiP layer thickness differential between right and left sides:~20 μ″

The shapes and flatnesses of resulting disks are shown in FIGS. 21A and26B (Type A disks) and FIGS. 27A through 32B (Type B disks). Theflatnesses of the disks are set forth below:

Type A disk 1 (FIGS. 21A-B) R-convex 5.645 microns disk 2 (FIGS. 22A-B)R-convex 2.870 microns disk 3 (FIGS. 23A-B) R-convex 4.808 microns disk4 (FIGS. 24A-B) R-convex 4.822 microns disk 5 (FIGS. 25A-B) R-convex5.317 microns disk 6 (FIGS. 26A-B) R-convex 4.192 microns

Type B disk 1 (FIGS. 27A-B) Irregular shape 0.617 microns disk 2 (FIGS.28A-B) R-convex 2.254 microns disk 3 (FIGS. 29A-B) R-concave 0.982microns disk 4 (FIGS. 30A-B) R-convex 1.358 microns disk 5 (FIGS. 31A-B)R-concave 2.926 microns disk 6 (FIGS. 32A-B) R-concave 2.234 microns

As can be seen from the above test results, Type-A disks exhibited all“cone”-shapes with higher flatness values whereas Type-B disks exhibitedsome “cone” shapes and some “bowl” shapes but with reduced flatnessvalues. Type-B disks were flatter than Type-A disks because Type-B diskshad a NiP layer thickness differential of around ˜20μ″ whereas Type-Adisks had a NiP layer thickness differential of around 0μ″. This NiPlayer thickness differential can be tailored to achieve specificflatnesses for specific applications, as noted previously.

The experimental results provided above show that pre-bent disks can beutilized in the magnetic media industry when one-side sputtering causesdisks to bend and form a convex shape due to compressive stressimbalance within the various layers/films. By depositing sputtered filmsonto the side of the substrate disk which is already bent to form aconcave shape (“bowl”-shape, looking to the side in question), the twobending tendencies in opposite directions (from the thicker NiP layer onone side of the disk and the thinner NiP layer and sputtered films onthe other side of the disk) are cancelled. The cancellation (orequalization) of the compressive stresses on both sides of the diskscause the resulting disks (after sputter) to be flatter.

A number of variations and modifications of the invention can be used.It would be possible to provide for some features of the inventionwithout providing others.

For example in one alternative embodiment, the present invention appliesto any form-factor disk, whether 95 mm, 84 mm, 65 mm, 48 mm, or 25 mm indiameter and 63 mil, 50 mil, 40 mil, 31.5 mil, or 25 mil in thickness.

In another alternative embodiment, the use of differential thicknessesof selected layers can be employed in dual-sided disks in whichdiffering cumulative intra-layer stresses are present on both sides ofthe disk. This situation can occur, for example, when differing types ornumbers of layers are located on both sides of the disk. By way ofillustration, one side of the disk can have one magnetic layer and theother side two magnetic layers or one side of the disk can have amagnetic layer having a different chemical composition than a magneticlayer on the other side of the disk. The stress imbalance can causewarping of the disk as previously noted. Differential thicknesses ofselected layers on the two sides of the disk can be used to reduce oreliminate the stress imbalance and therefore provide a more planar disk.

In yet another alternative embodiment, the thicknesses in the upper andlower selected layers 304 and 308 is effected during selected layerdeposition rather than or in addition to that effected during roughand/or fine polishing. In other words, differing thicknesses of selectedlayers are applied to the different sides of the disk.

In yet another alternative embodiment, pre-bending or pre-shaping of thesubstrate disk and selected layers can be accomplished using mechanicaltechniques (which cause the plated disk to defonn plastically), thermaltechniques, and combinations thereof.

The present invention, in various embodiments, includes components,methods, processes, systems and/or apparatus substantially as depictedand described herein, including various embodiments, subcombinations,and subsets thereof. Those of skill in the art will understand how tomake and use the present invention after understanding the presentdisclosure. The present invention, in various embodiments, includesproviding devices and processes in the absence of items not depictedand/or described herein or in various embodiments hereof, including inthe absence of such items as may have been used in previous devices orprocesses, e.g. for improving performance, achieving ease and orreducing cost of implementation.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. In theforegoing Detailed Description for example, various features of theinvention are grouped together in one or more embodiments for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed inventionrequires more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the followingclaims are hereby incorporated into this Detailed Description, with eachclaim standing on its own as a separate preferred embodiment of theinvention.

Moreover though the description of the invention has includeddescription of one or more embodiments and certain variations andmodifications, other variations and modifications are within the scopeof the invention, e.g. as may be within the skill and knowledge of thosein the art, after understanding the present disclosure. It is intendedto obtain rights which include alternative embodiments to the extentpermitted, including alternate, interchangeable and/or equivalentstructures, functions, ranges or steps to those claimed, whether or notsuch alternate, interchangeable and/or equivalent structures, functions,ranges or steps are disclosed herein, and without intending to publiclydedicate any patentable subject matter.

1. A method for producing an information-storage media disk having firstand second interface layers, a first information storage layer on afirst side of a substrate disk, and a second information storage layeron second side of the substrate disk, comprising: depositing the firstinterface layer on the first side of a substrate disk and the secondinterface layer on the second side of said substrate disk, respectively,wherein the first and second interface layers have differing chemicalcompositions, and wherein the first and second interface layers causethe substrate disk to be curved; controlling curvature of the disk byremoving unequal thicknesses from the first and second interface layers,wherein, after the removal step, the first and second interface layersremain, the thickness of the first interface layer being less than thethickness of the second interface layer and the flatness of the firstand second sides is from 2 to 10 microns; subsequently depositing thefirst information storage layer on the first interface layer and thesecond information storage layer on the second interface layer; andcontrolling curvature of the information-storage media by forming theinformation-storage layers and the first and second interface layers toprovide the information-storage media.
 2. The media of claim 1, whereinthe first and second interface layers comprise nickel phosphorus andwherein the other one of the first and second interface layers is notadjacent to the information-storage layer.
 3. The media of claim 1,wherein a first thickness of the first interface layer is no more thanabout 99.3% of a second thickness of the second interface layer.
 4. Themedia of claim 1, further comprising controlling curvature of theinformation-storage media by removing unequal thicknesses from the firstand second interface layers wherein after the removal flatness of thefirst and second sides is from about 2 to about 10 microns, and whereina first thickness of the first interface layer is no more than about99.3% of a second thickness of the second interface layer.
 5. The mediaof claim 1, wherein the information-storage layer is a ferromagneticmaterial, wherein the information-storage layer is adjacent to the firstinterface layer, and further comprising: an underlayer positionedbetween the information-storage layer and the first interface layer; andan overcoat layer, wherein the information-storage layer is positionedbetween the overcoat layer and the underlayer, wherein theinformation-storage layer and underlayer are each in compression.
 6. Themedia of claim 1, wherein the first and second interface layers have thesame chemical composition and wherein a compressive stress in the firstinterface layer is less than a compressive stress in the secondinterface layer.
 7. The media of claim 1, wherein theinformation-storage layer is adjacent to the second interface layer andthe second interface layer is located between the information-storagelayer and the substrate, wherein the first side is free of aninformation-storage layer, and, wherein the information-storage layer isin tension.
 8. The media of claim 1, wherein the first and secondinterface layers are each in tension and wherein the information-storagelayer is in compression.
 9. The media of claim 1, wherein depositingfirst and second interface layers on first and second sides comprises:depositing the first interface layer at a first thickness; anddepositing the second interface layer at a second thickness, wherein thefirst and second thicknesses are different.
 10. The media of claim 1,wherein depositing first and second interface layers on first and secondsides comprises: depositing the first and second interface layers on thesubstrate disk, wherein, after the depositing step, the thicknesses ofthe first and second interface layers are substantially the same. 11.The media of claim 1, wherein the removing step comprises: roughpolishing only one of the first and second sides of the first and secondinterface layers.
 12. The media of claim 1, wherein the removing stepcomprises: fine polishing only one of the first and second sides of thefirst and second interface layers.
 13. The media of claim 1, wherein theremoving step comprises: rough polishing only one of the first andsecond sides of the first and second interface layers to remove a firstthickness of the corresponding first and second interface layer; andfine polishing the only one of the first and second sides to remove asecond thickness of the corresponding first and second interface layer.